1. Field of the Invention
The present invention relates generally to a disk array subsystems adaptable for use as storage device in a computer system, and more particularly to a disk array subsystem for automatically performing self-reallocation of logical volumes without requiring any assistance by its associated host computer such as a host computer operatively connected thereto.
2. Description of the Prior Art
Conventionally, a magnetic disk subsystem carries important tasks in that it plays a significant role of the external storage device for a computer system. Especially, a disk array subsystem has become more important for applications as advanced magnetic disk subsystem with high reliability.
In general, the disk array subsystems are known as redundant array of inexpensive disks (RAIDs), which may be classified in five categories of different levels of from RAID1 to RAID5 based on the characteristics thereof. At present, of these five (5) levels, special attention is taken to the RAID5 architecture that may attain high reliability and wide applicability at lower cost and is thus expected to be adapted for use in the transaction processing essentially consisting of several small-capacity random access procedures. Typically, one prior known disk array subsystem includes a magnetic disk drive device for record and/or reproduction of data, a magnetic disk control device that controls the data transmission between the magnetic disk drive device and a host computer.
The magnetic disk drive device has therein a magnetic disk drive for recording data. The RAID5 architecture is designed to employ a specific format allowing a plurality of magnetic disk drives to be operatively combined into one group, which is then assumed to exhibit more than one logically defined volume (referred to as "logical volume" hereinafter).
In such disk array subsystem any enhancement of subsystem's capacity may be attained by additional installation of a magnetic disk drive(s) thus either providing a further logical volume or causing the logical volume to increase in capacity as a whole. However, in the situation where input/output (I/O) processing tasks tend to be concentrated on a specific logical volume, the I/O processings are to be locally directed or "focussed" onto a magnetic disk drive group being allocated with the said logical volume, resulting in an increase in the processing wait time of magnetic disk drives due to the occurrence of contention or conflict of the identical processings. This will possibly prevent the disk array subsystem from taking full advantage of it in performance.
Published Unexamined Japanese Patent Application (PUJPA) No. 6-161837 discloses therein an arrangement for choosing a volume selection scheme from among a group of volume selection schemes thus enabling them to be selectively utilized automatically as necessary. Due to the possibility of changing or modifying the optimal volume selection scheme, it is possible to accomplish effective file allocation for reduction of the concentration of I/O loads upon a specific volume.
As the information-oriented society is highly advanced, the amount of data it possesses is increasing more and more. Accordingly, the magnetic disk drives are strongly demanded to attain a further increase both in mass storage and in reliability. To meet such demand, a disk array subsystem that offers higher reliability is utilized; on the contrary, for the need to enhance the storage capacity, it has been one typical approach in the prior art to employ a mere method of simply adding magnetic drives while having to additionally install corresponding ones of logical volumes therefor or having to extend the logical volume in capacity.
Additionally, as the storage capacity increases, the concentration of I/O processings for a specific file will take place more frequently than ever. To avoid this problem, the prior art system attempts to use automated volume selection techniques achieving an effective allocation of files concerned.
Unfortunately, such prior art disk array subsystem is encountered with a problem as follows. When the logical volume per se is added, it is difficult when using the prior known file allocation method to avoid the concentration of I/O processings upon the same magnetic disk drive in the situation where the processing tasks are to be concentrated on a specific volume; it will be readily seen that the above difficulty results in the processing wait time being undesirably increased due to the occurrence of contention or conflict in a queue of several I/O processings, which may adversely serve to make it impossible to take full advantage of the subsystem's inherent performance.